firmware: scmi: mailbox/smt agent device

This change implements a mailbox transport using SMT format for SCMI
exchanges. This implementation follows the Linux kernel and
SCP-firmware [1] as references implementation for SCMI message
processing using SMT format for communication channel meta-data.

Use of mailboxes in SCMI FDT bindings are defined in the Linux kernel
DT bindings since v4.17.

Links: [1] https://github.com/ARM-software/SCP-firmware
Signed-off-by: Etienne Carriere <etienne.carriere@linaro.org>
Cc: Simon Glass <sjg@chromium.org>
Cc: Peng Fan <peng.fan@nxp.com>
Cc: Sudeep Holla <sudeep.holla@arm.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

drivers/firmware/scmi/Kconfig

@@ -2,7 +2,7 @@ config SCMI_FIRMWARE
 	bool "Enable SCMI support"
 	select FIRMWARE
 	select OF_TRANSLATE
-	depends on SANDBOX
+	depends on SANDBOX || DM_MAILBOX
 	help
 	  System Control and Management Interface (SCMI) is a communication
 	  protocol that defines standard interfaces for power, performance
@@ -14,4 +14,6 @@ config SCMI_FIRMWARE
 	  or a companion host in the CPU system.
 
 	  Communications between agent (client) and the SCMI server are
-	  based on message exchange.
+	  based on message exchange. Messages can be exchange over tranport
+	  channels as a mailbox device with some piece of identified shared
+	  memory.

drivers/firmware/scmi/Makefile

@@ -1,2 +1,4 @@
 obj-y	+= scmi_agent-uclass.o
+obj-y	+= smt.o
+obj-$(CONFIG_DM_MAILBOX)	+= mailbox_agent.o
 obj-$(CONFIG_SANDBOX)		+= sandbox-scmi_agent.o

drivers/firmware/scmi/mailbox_agent.c

@@ -0,0 +1,102 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2020 Linaro Limited.
+ */
+
+#include <common.h>
+#include <dm.h>
+#include <errno.h>
+#include <mailbox.h>
+#include <scmi_agent.h>
+#include <scmi_agent-uclass.h>
+#include <dm/devres.h>
+#include <linux/compat.h>
+
+#include "smt.h"
+
+#define TIMEOUT_US_10MS			10000
+
+/**
+ * struct scmi_mbox_channel - Description of an SCMI mailbox transport
+ * @smt:	Shared memory buffer
+ * @mbox:	Mailbox channel description
+ * @timeout_us:	Timeout in microseconds for the mailbox transfer
+ */
+struct scmi_mbox_channel {
+	struct scmi_smt smt;
+	struct mbox_chan mbox;
+	ulong timeout_us;
+};
+
+static int scmi_mbox_process_msg(struct udevice *dev, struct scmi_msg *msg)
+{
+	struct scmi_mbox_channel *chan = dev_get_priv(dev);
+	int ret;
+
+	ret = scmi_write_msg_to_smt(dev, &chan->smt, msg);
+	if (ret)
+		return ret;
+
+	/* Give shm addr to mbox in case it is meaningful */
+	ret = mbox_send(&chan->mbox, chan->smt.buf);
+	if (ret) {
+		dev_err(dev, "Message send failed: %d\n", ret);
+		goto out;
+	}
+
+	/* Receive the response */
+	ret = mbox_recv(&chan->mbox, chan->smt.buf, chan->timeout_us);
+	if (ret) {
+		dev_err(dev, "Response failed: %d, abort\n", ret);
+		goto out;
+	}
+
+	ret = scmi_read_resp_from_smt(dev, &chan->smt, msg);
+
+out:
+	scmi_clear_smt_channel(&chan->smt);
+
+	return ret;
+}
+
+int scmi_mbox_probe(struct udevice *dev)
+{
+	struct scmi_mbox_channel *chan = dev_get_priv(dev);
+	int ret;
+
+	chan->timeout_us = TIMEOUT_US_10MS;
+
+	ret = mbox_get_by_index(dev, 0, &chan->mbox);
+	if (ret) {
+		dev_err(dev, "Failed to find mailbox: %d\n", ret);
+		goto out;
+	}
+
+	ret = scmi_dt_get_smt_buffer(dev, &chan->smt);
+	if (ret)
+		dev_err(dev, "Failed to get shm resources: %d\n", ret);
+
+out:
+	if (ret)
+		devm_kfree(dev, chan);
+
+	return ret;
+}
+
+static const struct udevice_id scmi_mbox_ids[] = {
+	{ .compatible = "arm,scmi" },
+	{ }
+};
+
+static const struct scmi_agent_ops scmi_mbox_ops = {
+	.process_msg = scmi_mbox_process_msg,
+};
+
+U_BOOT_DRIVER(scmi_mbox) = {
+	.name		= "scmi-over-mailbox",
+	.id		= UCLASS_SCMI_AGENT,
+	.of_match	= scmi_mbox_ids,
+	.priv_auto_alloc_size = sizeof(struct scmi_mbox_channel),
+	.probe		= scmi_mbox_probe,
+	.ops		= &scmi_mbox_ops,
+};

drivers/firmware/scmi/smt.c

@@ -0,0 +1,139 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2015-2019, Arm Limited and Contributors. All rights reserved.
+ * Copyright (C) 2019-2020 Linaro Limited.
+ */
+
+#include <common.h>
+#include <cpu_func.h>
+#include <dm.h>
+#include <errno.h>
+#include <scmi_agent.h>
+#include <asm/cache.h>
+#include <asm/system.h>
+#include <dm/ofnode.h>
+#include <linux/compat.h>
+#include <linux/io.h>
+#include <linux/ioport.h>
+
+#include "smt.h"
+
+/**
+ * Get shared memory configuration defined by the referred DT phandle
+ * Return with a errno compliant value.
+ */
+int scmi_dt_get_smt_buffer(struct udevice *dev, struct scmi_smt *smt)
+{
+	int ret;
+	struct ofnode_phandle_args args;
+	struct resource resource;
+	fdt32_t faddr;
+	phys_addr_t paddr;
+
+	ret = dev_read_phandle_with_args(dev, "shmem", NULL, 0, 0, &args);
+	if (ret)
+		return ret;
+
+	ret = ofnode_read_resource(args.node, 0, &resource);
+	if (ret)
+		return ret;
+
+	faddr = cpu_to_fdt32(resource.start);
+	paddr = ofnode_translate_address(args.node, &faddr);
+
+	smt->size = resource_size(&resource);
+	if (smt->size < sizeof(struct scmi_smt_header)) {
+		dev_err(dev, "Shared memory buffer too small\n");
+		return -EINVAL;
+	}
+
+	smt->buf = devm_ioremap(dev, paddr, smt->size);
+	if (!smt->buf)
+		return -ENOMEM;
+
+#ifdef CONFIG_ARM
+	if (dcache_status())
+		mmu_set_region_dcache_behaviour((uintptr_t)smt->buf,
+						smt->size, DCACHE_OFF);
+#endif
+
+	return 0;
+}
+
+/**
+ * Write SCMI message @msg into a SMT shared buffer @smt.
+ * Return 0 on success and with a negative errno in case of error.
+ */
+int scmi_write_msg_to_smt(struct udevice *dev, struct scmi_smt *smt,
+			  struct scmi_msg *msg)
+{
+	struct scmi_smt_header *hdr = (void *)smt->buf;
+
+	if ((!msg->in_msg && msg->in_msg_sz) ||
+	    (!msg->out_msg && msg->out_msg_sz))
+		return -EINVAL;
+
+	if (!(hdr->channel_status & SCMI_SHMEM_CHAN_STAT_CHANNEL_FREE)) {
+		dev_dbg(dev, "Channel busy\n");
+		return -EBUSY;
+	}
+
+	if (smt->size < (sizeof(*hdr) + msg->in_msg_sz) ||
+	    smt->size < (sizeof(*hdr) + msg->out_msg_sz)) {
+		dev_dbg(dev, "Buffer too small\n");
+		return -ETOOSMALL;
+	}
+
+	/* Load message in shared memory */
+	hdr->channel_status &= ~SCMI_SHMEM_CHAN_STAT_CHANNEL_FREE;
+	hdr->length = msg->in_msg_sz + sizeof(hdr->msg_header);
+	hdr->msg_header = SMT_HEADER_TOKEN(0) |
+			  SMT_HEADER_MESSAGE_TYPE(0) |
+			  SMT_HEADER_PROTOCOL_ID(msg->protocol_id) |
+			  SMT_HEADER_MESSAGE_ID(msg->message_id);
+
+	memcpy_toio(hdr->msg_payload, msg->in_msg, msg->in_msg_sz);
+
+	return 0;
+}
+
+/**
+ * Read SCMI message from a SMT shared buffer @smt and copy it into @msg.
+ * Return 0 on success and with a negative errno in case of error.
+ */
+int scmi_read_resp_from_smt(struct udevice *dev, struct scmi_smt *smt,
+			    struct scmi_msg *msg)
+{
+	struct scmi_smt_header *hdr = (void *)smt->buf;
+
+	if (!(hdr->channel_status & SCMI_SHMEM_CHAN_STAT_CHANNEL_FREE)) {
+		dev_err(dev, "Channel unexpectedly busy\n");
+		return -EBUSY;
+	}
+
+	if (hdr->channel_status & SCMI_SHMEM_CHAN_STAT_CHANNEL_ERROR) {
+		dev_err(dev, "Channel error reported, reset channel\n");
+		return -ECOMM;
+	}
+
+	if (hdr->length > msg->out_msg_sz + sizeof(hdr->msg_header)) {
+		dev_err(dev, "Buffer to small\n");
+		return -ETOOSMALL;
+	}
+
+	/* Get the data */
+	msg->out_msg_sz = hdr->length - sizeof(hdr->msg_header);
+	memcpy_fromio(msg->out_msg, hdr->msg_payload, msg->out_msg_sz);
+
+	return 0;
+}
+
+/**
+ * Clear SMT flags in shared buffer to allow further message exchange
+ */
+void scmi_clear_smt_channel(struct scmi_smt *smt)
+{
+	struct scmi_smt_header *hdr = (void *)smt->buf;
+
+	hdr->channel_status &= ~SCMI_SHMEM_CHAN_STAT_CHANNEL_ERROR;
+}

drivers/firmware/scmi/smt.h

@@ -0,0 +1,86 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (c) 2015-2019, Arm Limited and Contributors. All rights reserved.
+ * Copyright (C) 2019-2020 Linaro Limited.
+ */
+#ifndef SCMI_SMT_H
+#define SCMI_SMT_H
+
+#include <asm/types.h>
+
+/**
+ * struct scmi_smt_header - Description of the shared memory message buffer
+ *
+ * SMT stands for Shared Memory based Transport.
+ * SMT uses 28 byte header prior message payload to handle the state of
+ * the communication channel realized by the shared memory area and
+ * to define SCMI protocol information the payload relates to.
+ */
+struct scmi_smt_header {
+	__le32 reserved;
+	__le32 channel_status;
+#define SCMI_SHMEM_CHAN_STAT_CHANNEL_ERROR	BIT(1)
+#define SCMI_SHMEM_CHAN_STAT_CHANNEL_FREE	BIT(0)
+	__le32 reserved1[2];
+	__le32 flags;
+#define SCMI_SHMEM_FLAG_INTR_ENABLED		BIT(0)
+	__le32 length;
+	__le32 msg_header;
+	u8 msg_payload[0];
+};
+
+#define SMT_HEADER_TOKEN(token)		(((token) << 18) & GENMASK(31, 18))
+#define SMT_HEADER_PROTOCOL_ID(proto)	(((proto) << 10) & GENMASK(17, 10))
+#define SMT_HEADER_MESSAGE_TYPE(type)	(((type) << 18) & GENMASK(9, 8))
+#define SMT_HEADER_MESSAGE_ID(id)	((id) & GENMASK(7, 0))
+
+/**
+ * struct scmi_smt - Description of a SMT memory buffer
+ * @buf:	Shared memory base address
+ * @size:	Shared memory byte size
+ */
+struct scmi_smt {
+	u8 *buf;
+	size_t size;
+};
+
+static inline bool scmi_smt_channel_is_free(struct scmi_smt *smt)
+{
+	struct scmi_smt_header *hdr = (void *)smt->buf;
+
+	return hdr->channel_status & SCMI_SHMEM_CHAN_STAT_CHANNEL_FREE;
+}
+
+static inline bool scmi_smt_channel_reports_error(struct scmi_smt *smt)
+{
+	struct scmi_smt_header *hdr = (void *)smt->buf;
+
+	return hdr->channel_status & SCMI_SHMEM_CHAN_STAT_CHANNEL_ERROR;
+}
+
+static inline void scmi_smt_get_channel(struct scmi_smt *smt)
+{
+	struct scmi_smt_header *hdr = (void *)smt->buf;
+
+	hdr->channel_status &= ~SCMI_SHMEM_CHAN_STAT_CHANNEL_FREE;
+}
+
+static inline void scmi_smt_put_channel(struct scmi_smt *smt)
+{
+	struct scmi_smt_header *hdr = (void *)smt->buf;
+
+	hdr->channel_status |= SCMI_SHMEM_CHAN_STAT_CHANNEL_FREE;
+	hdr->channel_status &= ~SCMI_SHMEM_CHAN_STAT_CHANNEL_ERROR;
+}
+
+int scmi_dt_get_smt_buffer(struct udevice *dev, struct scmi_smt *smt);
+
+int scmi_write_msg_to_smt(struct udevice *dev, struct scmi_smt *smt,
+			  struct scmi_msg *msg);
+
+int scmi_read_resp_from_smt(struct udevice *dev, struct scmi_smt *smt,
+			    struct scmi_msg *msg);
+
+void scmi_clear_smt_channel(struct scmi_smt *smt);
+
+#endif /* SCMI_SMT_H */